Telephone transmitter



A 5 1927. L-fisggss H. H. C. DUNWOODY TELEPHONE TRANSMITTER Filed May 29, 1924 J9 ayzw'y a;

Patented Aug. 9, 1927.

UNITED STATES.

PATENT OFFICE.

TELEPHONE 'rRANsMrrrnn.

Application filed May 29,

My invention relates broadly to the electrical transmission of sound, and more particularly to an improved form of telephone transmitter and repeater.

One of the objects of my invention is to improved the quality of articulation of speech which may be transmitted through an electrical circuit to control either a line wire system or a modulation circuit or" a radio system.

Still another object of my invention is to provide a microphonic contact system distributed over an area against which the sound waves to be electrically reproduced may be impinged to secure a positive electrical variation in the electrical circuit con trolled by the transmitting system.

Still another object'of my invention is to provide a construction of voice modulation device including a pair of conductive plates substantially separated one from the other by a plurality of microphonic contacts distributed throughout the area 01": the plates and the plates positioned within an'intense magnetic field whereby movement of the. conductive plates under vibrations of the voice causes energy to be generated in the plates which energy is modulated-by the microphonic contact and usefully employed in an electrical circuit for transmitted sound electrically. g Y '7 Still another object of my invention is to provide a construction of telephone transmitter or repeater in which the voicevibrations directly cause the generation of energy in an electrical circuit which energy is usefully employed in modulating the transmitting circuit. 7

My invention will be more fully understood from the specification hereinafter following by reference to the accompanying drawings in which: v

Figure 1 is a partial cross sectional View taken throughone construction of my improved telephone transmitter showing the arrangement of the plurality of microphonic contacts which I employ;

Figure 2 is a perspective view illustratingthe electrically conductive plates employed in the telephone transmitter of my invention separated by a di-electric sheet which forms a spacing element for the microphonic contacts employed-in the device;

Figure 3 is a theoretical diagram illus- 1924. Serial No. 716,766.

trating the intense magnetic field created in the telephone transmitter and in which the multiple diaphragm construction is vibrated by voice vibrations to thereby generate energy in the conductors which energy is c .modulated in accordance with the voice for controlling the transmitting circuit;

Figure t'illustrates a telephone line wire subscriber circuit employmg the transmitter construction of my invention;

Figure 5 is a theoretical diagram illustrating the principle of the telephone transmitter of my invention as applied to a line Wire system;

Figure 6 illustrates the telephone transmitter of my invention as applied to a modulating circuit of a radio transmitter;

Figure 7 illustrates the application of my invention to repeater circuits for line wire systems; and ,6

Figure 8 is a detailed View of the repeater construction illustrated in Figure 7.

Ret'erring to thedrawings in detail referen'ce character-"1 indicates a casing. for the telephone transmitter of my invention hav-e ing a depending lug 2 at the rear thereof for securing the transmitter in any desired position; Acover member 3 is providedwhich substantially encloses the telephone trans;

mitter as a unit, positioning mouth piece l with reference to the interiormechanism of the transmitter. in The transmitter contains a strong permanent magnet .5 and central pole piece 9 upon which are disposed windings of an induction coil 6. These windings comprise secondary winding 7 and primary winding 8 and while operating as an induction coil as in theusual telephone subscriber system also sets up an intense magnetic field represented in Figure 3; by theoretical-lines 10 passing out'of the pole piece 9 into the permanent magnet member 5. I employ a multiple diaphragm construction including a pair of conductive plates 11 and 12,,whic

may be of carbon or a metal alloy or a metal whichfis susceptible to the maximum magnetism. The diaphragms may be permanently magnetized in such manner asto be constantly attracted toward each other. The multiple diaphragm is contained within a peripheral ring member 14 whichmay be of suitable resilient material and the plates 11 and 12 spaced apart therein by means of gaskets lti and17 on'either side of an insulated diaphragm 15. The insulated diaphragm 15 contains a plurality of apertures disposed throughout its area. as represented at 18 in Figure 2. In each of the apertures there is located a carbon microphonic contact 20. Each of the Inicrophonic contacts 20 is in the form of a short cylindrical member and is free to move within the apertures 18 which are slightly larger than the microphonic contacts 20. These microphonic contact members 20 are positioned with their faces in contact with the conductiveplates 11 and 12 and are relatively loosely maintained in position electrically closing the circuit between the plates 11 and 12 but in such a manner that as voice vibrations impinge against the area of one of the plates said contact becomes lighter or heavier as the case may be and tends to vary the resistance or the electrical circuit in which the plates 11 and 12 may be contained.

Referring to Figure 3 the induction coil windings 7 and 8 set up an intense magnetic field which emanates from the pole piece 9 the magnetic lines traveling into the permanent magnet 5 as represented at 10. The voice vibrations impinging against the plate 11 move the plates 11 and 12 within this magnetic field and tend to generatecurrent in these conductors operating to set up a difference in potential between plate 11 and plate 12. The energy thereby developed is varied in amplitude in accordance with the change in contact pressure between plates 11 and 12 and the carbon buttons 20 as the microphonic contacts throughout the area of the plates change under voice frequency. The plates 11 and 12 are included in a talking circuit as represented in Figure 4 where primary winding 21 of a transformer is represented as connected across plates 11 and 12. All current variations in primary winding 21 are impressed upon a.

secondary winding 22 in serieswith battery 23 and the primary and secondary windings 7 and 801? the usual induction coil 6 in a telephone system. The induction coils 7 and 8 are'connected as usual in the telephone receiver circuit-24 and line circuit 25. The transmitter circuit is closed through contacts 26 and hook switch 27 normally in contact with ringing circuit 28. It will be observed that the primary and secondary windings 7 and 8 are positioned with reference to the diaphragms 11 and 12 in such a manner as to set up a magnetic field of force which magnetic field is usefully employed as the voice vibrations are impressed against the diaphragms 11 and 12 in order to generate energy in-the circuit including the diaphragms 11 and 12. The principle involved in the electrical circuit is. more clearly represented in Figure 5 wherein the ing 30 to which is inductively related the winding 31. The winding 31 is connected across the diaphragms 11 and 12. The diaphragms 11 and 12 are so located with reference to an intense magnetic field 32 energized from battery 33 that'any'vibrations against the diaphragms 11 and 12 arising out of variations in voice frequency cause charges to be developed in plates 11 and 12 developing an electromotive force across the said plates which is varied by the change in conductivity of the microphonic contacts 20, to produce variations in winding 31 and corresponding variations in winding 30 to modulate the line system 29. I Figure 6 illustrates my invention as applied to a radio system in which the winding 31, illustrated in Figure 5, is inductively re lated to the, winding 30 and connected in the input circuit of modulator 34. The modu- H lator may be connected to a speech amplifier 35 which is in turn connected to an oscillator 36. A power amplifier 37 may be included in the system connected with an antenna 38 and ground connection 39 upon which the modulated signals from the micro} phonic contact device are impressed.

My microphonic contact system is applicable to telephone repeaters as well as telephone transmitters as will be understood by reference to Figures 7 and 8. The line wire system 40 includes windingsf41 and 42 to which windings 43 and 44 are inductively related. The repeater comprises'primary and secondary windings 46' and 47 in circuit with 3' battery 48'which windings operate upon solenoid plunger 50 which is "ejected against diaphragms ll and 12 by meansof screw adjustment 49 and spring 51. The diaphragms 11 and 12 may besp'aced apart :by the. microphonic contact members 20 as heretofore eXplaineda-nd the diaphragms may be electrically connected in circuit with battery 45.

The windings 46 and 47 "are electrically 7 arranged in regenerative relationship with? respect to the microphonic contact" device formed by plates 11 and 12 and contactimem ber 20 so that sound vibrations which impinge against conductive plate llset up elec- 1 trical impulses which are reamplified through windings 46 and 47 and then impressed on line circuit 40. The clear articulation se cured in the microphonic contact system of 1 my invention enables this device to be ap 199 plied as a repeater in the manner described:

to increase the amplitude of the speech currents upon the line or other circuit. A chopper 33 may be included in the circuits shown in Figs. 5 and 6 for securing a rapid 1. building up and collapse of the lines of force across plates 11 and 12 assi'mulatinglthe er fects of the induction coil windings 7 and 8 in Figures 1 and 4. The-arrangement'of circuits in the modulating system is such that re-amplification of the energy may be secured for increasing the amplitude of the energy in the system.

I have represented the microphoniccontact system in one of its preferred embodiments but it will be understood that modificartions may be made and that no limitations upon the invention are intended other than are imposed by the scope of the appended claims.

Having thus described my invention, what I claim and desire to secure bv Letters Patent of the United States, is as follows:

1. A telephone transmitter comprising in combination a pair of electrically conductive plates, means for conveying speech vibrations directly against one of said plates, 'a microphonic contact member, an insulating plate positioned between said conductive plates and apertured to provide a guide for said microphonic cont-act member within the apertured portion of said insulating plate and between said electrically conductive plates. l V

2. A telephone transmitter comprising in combination a pair of electrically conductive plates, means for conveylng speech v1- brations directly upon one of said plates,

an apertured insulating plate positioned between said conductive plates and substantially insulating one from the other and a microphonic contact member movably located within said apertured insulating plate and adjacent said electrically conductive plates.

3. A telephone transmitter comprising in combination a pair of electrically conductive conductive plates, means for directing speech vibrations immediately against one of said plates, an apertured insulating plate positioned between said conductive plates and substantially insulating one from the other and a' pluralityof microphonic contacts located in position by said apertured insulating plate and distributed throughout the .area thereof each of said contacts having their opposite faces adjacent said conductive plates and each being free to move independently with respect to said insulating plate. I

HENRY H. C. DUNWOODY. 

